Fluid catalytic cracking (FCC) is a hydrocarbon conversion process accomplished by contacting hydrocarbons in a fluidized reaction zone with a catalyst composed of finely divided particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the substantial absence of added hydrogen or the consumption of hydrogen. As the cracking reaction proceeds, substantial amounts of highly carbonaceous material referred to as coke is deposited on the catalyst. Conventionally, a high temperature regeneration operation within a regenerator zone is used to combust coke from the catalyst, thereby regenerating the catalyst. Catalyst containing coke, referred to herein as spent catalyst, is continually removed from the reaction zone and replaced by essentially coke-free catalyst from the regeneration zone. Fluidization of the catalyst particles by various gaseous streams allows the transport of catalyst between the reaction zone and regeneration zone.
A common objective of these configurations is maximizing product yield from the reactor while minimizing operating and equipment costs. Optimization of feedstock conversion ordinarily requires essentially complete removal of coke from the catalyst. This essentially complete removal of coke from catalyst is often referred to as complete regeneration. In order to obtain complete regeneration, the catalyst has to be in contact with oxygen for sufficient residence time to permit thorough combustion.
Conventional catalyst regenerators typically include a vessel having a spent catalyst inlet, a regenerated catalyst outlet and a combustion gas distributor for supplying air or other oxygen-containing gas to the bed of catalyst that resides in the vessel. Cyclone separators remove catalyst entrained in a flue gas before the gas exits the regenerator vessel. The interior of the vessel conventionally includes some refractory material that serves to insulate the vessel from its contents. However, portions of the vessel typically have areas of stagnant catalyst, which results in low temperatures at or near portions of the vessel walls. In some instances, temperatures at or near the vessel walls may be about 200° F. (about 93° C.) or less. This is a problem because the dew point for condensation of sulfuric acid under typical catalyst regeneration operating conditions is on the order of about 400° F. (about 204° C.). Thus, conventional catalyst regenerators operate under conditions whereby sulfuric acid can condense on or near a vessel wall, and corrode the vessel wall.
Accordingly, it is desirable to provide catalyst regeneration methods and apparatuses with corrosion inhibition. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and appended claims, taken in conjunction with the accompanying drawings and this background of the invention.